In a large bowl, cream butter and cream cheese until fluffy. Gradually add the flour and mix well.

Turn onto lightly floured surface; knead until smooth, about 3 minutes. Divide dough into fourths; cover and refrigerate for 1-2 hours or until easy to handle.

In a microwave, melt chocolate chips and milk; stir until smooth. Stir in walnuts. Cool to room temperature.

Roll out each portion of dough onto an ungreased baking sheet into an 11-in. x 6-1/2-in. rectangle. Spread 3/4 cup chocolate filling down the center of each rectangle. Fold long sides to the center; press to seal all edges. Turn over so the seam sides are down.

Bake at 350° for 27-32 minutes or until lightly browned. Remove to wire racks to cool. Cut into 1/2-in. slices. Dust with confectioners' sugar if desired.